The Toyota Prius is a full hybrid electric mid-size hatchback, formerly a compact sedan developed and manufactured by Toyota. The EPA and California Air Resources Board (CARB) rate the Prius as among the cleanest vehicles sold in the United States based on smog-forming emissions. In 2011, Toyota expanded the Toyota Prius Hybrid family to include the Toyota Prius v, an extended hatchback wagon, and the Prius c, a subcompact hatchback. The production version of the Prius plug-in hybrid was released in 2012. The Toyota Prius family reached global cumulative sales of 3.8 million units by June 2013, representing 71.7% of Toyota hybrid sales of 5.3 million Lexus and Toyota units sold worldwide since 1997. Global sales of the Toyota Prius c family passed the 500,000 mark in August 2013, with sales led by Japan with 448,703 Aquas, followed by the U.S. with 65,583 Prii c.
Toyota Prius Hybrid Design and Technology
The Toyota Prius Hybrid is a power-split or series-parallel (full) hybrid, sometimes referred to as a combined hybrid, a vehicle that can be propelled by gasoline and/or electric power. Wind resistance is reduced by a drag coefficient of 0.25 (0.29 for 2000 model) with a Kammback design to reduce air resistance. Lower rolling-resistance tires are used to reduce road friction. An electric water pump eliminates serpentine belts. In the U.S. and Canada, a vacuum flask is used to store hot coolant when the vehicle is powered off for reuse so as to reduce warm-up time. The Prius engine makes use of the Atkinson cycle.
Toyota Prius Hybrid EV Mode
When the vehicle is turned on with the “Power” button, it is ready to drive immediately with the electric motor, while electric pumps warm the engine with previously saved hot engine coolant before the internal combustion engine is started. The delay between powering the car on and starting the internal combustion engine is approximately seven seconds. A button labelled “EV” maintains Electric Vehicle mode after being powered on and under most low-load conditions at less than 25 mph (40 km/h). This permits driving with low noise and no fuel consumption for journeys under 1 mile (1.6 km). The car automatically reverts to normal mode if the battery becomes exhausted. Prior to the 2010 model, the North American model did not have the “EV” button, although the “EV” mode is still supported internally by the Prius Hybrid Vehicle management computer.
Toyota Prius Hybrid Batteries
There are two principal battery packs, the High Voltage (HV) battery, also known as the traction battery, and a 12 volt battery known as the Low Voltage (LV) battery. The traction battery is a sealed 38-module nickel metal hydride (NiMH) battery pack providing 273.6 volts, 6.5 A·h capacity and weighing 53.3 kg (118 lb) is supplied by Japan’s Panasonic EV Energy Co. They are normally charged between 40–60% of maximum capacity to prolong battery life as well as allow headroom for regenerative braking. Each battery pack uses 10–15 kg (22–33 lb) of lanthanum, and each Prius electric motor contains 1 kg (2 lb) of neodymium; production of the car is described as “the biggest user of rare earths of any object in the world.” The LV battery is essential to starting the car, providing initial power to the computer.
The Second Generation Toyota Prius Hybrid contains a 1.310kWh battery, composed of 28 modules. Each battery module is made of 6 individual 1.2v 6.5Ah Prismatic NiMH cells in series forming a 7.2v 6.5Ah module. Each module contains an integrated charge controller and relay. These modules are connected 28 in series to form a 201.6v 6.5Ah battery (traction battery), also known as the energy storage system. The computer controlled charge controller and battery management computer systems keep this battery between 38% and 82% state of charge, with a tendency to keep the average state of charge around 60%. By shallow cycling the battery only a small portion of its net available energy storage capacity is available for use (approximately 400Wh) by the hybrid drive system, but the shallow computer controlled cycling dramatically improves the cycle life, thermal management control, and net long term calendar life of the battery. Active cooling of this battery is achieved by a blower motor and air ducting, while passive thermal management was accomplished through the metal case design.
Toyota Prius Hybrid Battery Life Cycle
As the Toyota Prius Hybrid reached ten years of being available in the U.S. market, in February 2011 Consumer Reports decided to look at the lifetime of the Prius battery and the cost to replace it. The magazine tested a 2002 Toyota Prius with over 200,000 miles on it, and compared the results to the nearly identical 2001 Toyota Prius with 2,000 miles tested by Consumer Reports 10 years before. The comparison showed little difference in performance when tested for fuel economy and acceleration. Overall fuel economy of the 2001 model was 40.6 miles per US gallon (5.79 L/100 km; 48.8 mpg-imp) while the 2002 Toyota Prius with high mileage delivered 40.4 miles per US gallon (5.82 L/100 km; 48.5 mpg-imp).
The magazine concluded that the effectiveness of the battery has not degraded over the long run. The cost of replacing the battery varies between US$2,200 and US$2,600 from a Toyota dealer, but low-use units from salvage yards are available for around US$500. One study indicates it may be worthwhile to rebuild batteries using good blades from defective used batteries.
Toyota Prius Hybrid Electromagnetic Field levels
The Toyota Prius Hybrid uses electric motors in the hybrid propulsion systems, powered by a high voltage battery in the rear of the car. There has been some public concern over whether the levels of electromagnetic field exposure within the cabin are higher than comparable cars, and what health effects those fields may present, popularized by a 2008 The New York Times article. However, Toyota and several independent studies have indicated that aside from a brief spike when accelerating, the electromagnetic fields within the Toyota Prius Hybrid are no different from those of a conventional car and do not exceed the ICNIRP exposure guidelines.